We use a mix of Compaq and Dell here at work. I don't have much experience with the Compaq, but I have been VERY impressed with the Dell on-site support. If you are talking business-level servers, then I'd say Dell does a good job. If you are talking about a server for home-use or small business file sharing, then I'm not sure. That 4-hour response on-site support doesn't come cheap I'm sure, so it's probably not practical for home or small business use.
But, Dell stuff is black, which makes it SO much cooler than anything else (aside from maybe Sun...)